Basic AP 16

1. Chapter 1: ENDOCRINE SYSTEM 1
• Communication is a process in which a
sender transmits signals to one or
more receivers to control and
coordinate actions.
• In the human body, two major organ
systems participate in relatively “long
distance” communication: the
nervous system and the endocrine
system.
• Together, these two systems are
primarily responsible for maintaining
homeostasis in the body.
• The nervous system uses two types of
intercellular communication—
electrical and chemical signaling.
• The endocrine system uses just one
method of communication: chemical
signaling.
• In general, the nervous system
involves quick responses to rapid
changes in the external environment.
• The endocrine system is usually
slower acting—taking care of the
internal environment of the body,
maintaining homeostasis, and
controlling reproduction.

2. FIGHT OR FLIGHT 2
• So how does the fight-or-flight
response that was mentioned earlier
happen so quickly if hormones are
usually slower acting? It is because
the two systems are connected. It is
the fast action of the nervous system
in response to the danger in the
environment that stimulates the
adrenal glands to secrete their
hormones. As a result, the nervous
system can cause rapid endocrine
responses to keep up with sudden
changes in both the external and
internal environments when
necessary.

3. ENDOCRINE STRUCTURES 3
• The endocrine system consists of cells,
tissues, and organs that secrete
hormones as a primary or secondary
function.
• The endocrine gland is the major player
in this system.
• The primary function of these ductless
glands is to secrete their hormones
directly into the surrounding fluid. The
interstitial fluid and the blood vessels
then transport the hormones throughout
the body. The endocrine system includes
the pituitary, thyroid, parathyroid,
adrenal, and pineal glands.
• Some of these glands have both
endocrine and non-endocrine functions.

4. EXOCRINE SYSTEM 4
• The ductless endocrine glands
are not to be confused with the
body’s exocrine system, whose
glands release their secretions
through ducts.
• Examples of exocrine glands
include the sebaceous and sweat
glands of the skin.

5. HORMONES 5
• Although a given hormone may travel throughout
the body in the bloodstream, it will affect the
activity only of its target cells; that is, cells with
receptors for that particular hormone.
• Once the hormone binds to the receptor, a chain of
events is initiated that leads to the target cell’s
response.
• Hormones play a critical role in the regulation of
physiological processes because of the target cell
responses they regulate.
• These responses contribute to human
reproduction, growth and development of body
tissues, metabolism, fluid, and electrolyte balance,
sleep, and many other body functions.
• The major hormones of the human body and their
effects are identified in Table 17.2.
Pituitary
(anterior)
Growth hormone
(GH)
Protein Promotes growth of body tissues
Pituitary
(anterior)
Prolactin (PRL) Peptide Promotes milk production
Pituitary
(anterior)
Thyroid-stimulating
hormone (TSH)
Glycoprotein Stimulates thyroid hormone release

6. MORE HORMONES 6
Pituitary
(anterior)
Adrenocorticotropic
hormone (ACTH)
Peptide Stimulates hormone release by adrenal cortex
Pituitary
(anterior)
Follicle-stimulating
hormone (FSH)
Glycoprotein Stimulates gamete production
Pituitary
(anterior)
Luteinizing hormone
(LH)
Glycoprotein Stimulates androgen production by gonads
Pituitary
(posterior)
Antidiuretic hormone
(ADH)
Peptide Stimulates water reabsorption by kidneys
Pituitary
(posterior)
Oxytocin Peptide Stimulates uterine contractions during childbirth
Thyroid
Thyroxine (T4),
triiodothyronine (T3)
Amine Stimulate basal metabolic rate
Thyroid Calcitonin Peptide Reduces blood Ca2+ levels
Parathyroid
Parathyroid
hormone (PTH)
Peptide Increases blood Ca2+ levels
Adrenal
(cortex)
Aldosterone Steroid Increases blood Na+ levels
Adrenal
(cortex)
Cortisol,
corticosterone,
cortisone
Steroid Increase blood glucose levels
Adrenal
(medulla)
Epinephrine,
norepinephrine
Amine Stimulate fight-or-flight response
Pineal Melatonin Amine Regulates sleep cycles
Pancreas Insulin Protein Reduces blood glucose levels
Pancreas Glucagon Protein Increases blood glucose levels
Testes Testosterone Steroid
Stimulates development of male secondary sex
characteristics and sperm production
Ovaries
Estrogens and
progesterone
Steroid
Stimulate development of female secondary sex
characteristics and prepare the body for childbirth

7. Types of Hormones 7
• The hormones of the human
body can be divided into two
major groups on the basis of
their chemical structure.
• Hormones derived from amino
acids include amines, peptides,
and proteins.
• Those derived from lipids
include steroids.

8. Role of Feedback Loops 8
• Positive feedback loops are
characterized by the release of
additional hormone in response to an
original hormone release.
• The release of oxytocin during
childbirth is a positive feedback loop.
• The more common method of
hormone regulation is the negative
feedback loop.
• Negative feedback is characterized by
the inhibition of further secretion of a
hormone in response to adequate
levels of that hormone. This allows
blood levels of the hormone to be
regulated within a narrow range. An
example of a negative feedback loop
is the release of glucocorticoid
hormones from the adrenal glands, as
directed by the hypothalamus and
pituitary gland.

9. Hypothalamus-Pituitary 9
• The hypothalamus–pituitary complex can
be thought of as the “command center”
of the endocrine system.
• This complex secretes several hormones
that directly produce responses in target
tissues, as well as hormones that regulate
the synthesis and secretion of hormones
of other glands.
• In addition, the hypothalamus–pituitary
complex coordinates the messages of the
endocrine and nervous systems.
• In many cases, a stimulus received by the
nervous system must pass through the
hypothalamus–pituitary complex to be
translated into hormones that can initiate
a response.
• The posterior pituitary gland does not
produce hormones, but rather stores and
secretes hormones produced by the
hypothalamus.

10. Pituitary Gland 10
• Antidiuretic hormone (ADH):
hypothalamic hormone that is
stored by the posterior pituitary
and that signals the kidneys to
reabsorb water and contributes
to the regulation of the body’s
fluid and electrolyte balance.

11. Oxytocin 11
• Oxytocin: stimulates uterine
contractions and dilation of the
cervix during childbirth.
• First, oxytocin is necessary for
the milk ejection reflex
(commonly referred to as “let-
down”) in breastfeeding women.
• Oxytocin is also thought to be
involved in feelings of love and
closeness, as well as in the
sexual response.

12. Thyroid Gland 12
• A butterfly-shaped organ, the thyroid gland is
located anterior to the trachea, just inferior to the
larynx.
• The medial region, called the isthmus, is flanked by
wing-shaped left and right lobes.
• Each of the thyroid lobes are embedded with
parathyroid glands, primarily on their posterior
surfaces. The tissue of the thyroid gland is
composed mostly of thyroid follicles.
• The follicles are made up of a central cavity filled
with a sticky fluid called colloid.
• Surrounded by a wall of epithelial follicle cells, the
colloid is the center of thyroid hormone
production, and that production is dependent on
the hormone’s essential and unique component:
iodine.
• The thyroid secretes 3 hormones: Thyroxine (T4),
Triiodothyronine (T3), and Calcitonin.

13. Parathyroid 13
• The parathyroid glands are tiny, round
structures usually found embedded in the
posterior surface of the thyroid gland.
• The parathyroid glands produce and
secrete PTH, a peptide hormone, in
response to low blood calcium levels.
• PTH secretion causes the release of
calcium from the bones by stimulating
osteoclasts, which secrete enzymes that
degrade bone and release calcium into
the interstitial fluid.
• A negative feedback loop regulates the
levels of PTH, with rising blood calcium
levels inhibiting further release of PTH.

14. Adrenal Glands 14
• The adrenal glands have a rich blood
supply and experience one of the highest
rates of blood flow in the body.
• One of the major functions of the adrenal
gland is to respond to stress. Stress can
be either physical or psychological or
both.
• Physical stresses include exposing the
body to injury, walking outside in cold and
wet conditions without a coat on, or
malnutrition.
• Psychological stresses include the
perception of a physical threat, a fight
with a loved one, or just a bad day at
school.

15. Adrenal Glands: GAS 15
• The body responds in different ways to short-term
stress and long-term stress following a pattern
known as the general adaptation syndrome (GAS).
• Once this stress is relieved, the body quickly
returns to normal. The section on the adrenal
medulla covers this response in more detail.
• If the stress is not soon relieved, the body adapts
to the stress in the second stage called the stage of
resistance. If a person is starving for example, the
body may send signals to the gastrointestinal tract
to maximize the absorption of nutrients from food.
• If the stress continues for a longer term however,
the body responds with symptoms quite different
than the fight-or-flight response. During the stage
of exhaustion, individuals may begin to suffer
depression, the suppression of their immune
response, severe fatigue, or even a fatal heart
attack.

16. Pineal Gland 16
• The pineal gland, a tiny endocrine gland
whose functions are not entirely clear.
• The pinealocyte cells that make up the
pineal gland are known to produce and
secrete the amine hormone melatonin,
which is derived from serotonin.
• The secretion of melatonin varies
according to the level of light received
from the environment.
• The secretion of melatonin may influence
the body’s circadian rhythms, the dark-
light fluctuations that affect not only
sleepiness and wakefulness, but also
appetite and body temperature.

17. Reproductive Hormones 17
Gonad
Associated
hormones
Chemical
class
Effect
Testes Testosterone Steroid
Stimulates development of male secondary sex characteristics and
sperm production
Testes Inhibin Protein Inhibits FSH release from pituitary
Ovaries
Estrogens and
progesterone
Steroid
Stimulate development of female secondary sex characteristics and
prepare the body for childbirth
Placenta
Human chorionic
gonadotropin
Protein
Promotes progesterone synthesis during pregnancy and inhibits
immune response against fetus

18. Pancreas 18
• The pancreas is a long, slender
organ, most of which is located
posterior to the bottom half of the
stomach.
• Although it is primarily an exocrine
gland, secreting a variety of
digestive enzymes, the pancreas
has an endocrine function. Its
pancreatic islets—clusters of cells
formerly known as the islets of
Langerhans—secrete the
hormones glucagon, insulin,
somatostatin, and pancreatic
polypeptide

19. Pancreatic Islets 19
• The pancreatic islets each contain four varieties of cells:
• The alpha cell produces the hormone glucagon and makes up
approximately 20 percent of each islet. Glucagon plays an
important role in blood glucose regulation; low blood glucose
levels stimulate its release.
• The beta cell produces the hormone insulin and makes up
approximately 75 percent of each islet. Elevated blood
glucose levels stimulate the release of insulin.
• The delta cell accounts for four percent of the islet cells and
secretes the peptide hormone somatostatin. Recall that
somatostatin is also released by the hypothalamus (as GHIH),
and the stomach and intestines also secrete it. An inhibiting
hormone, pancreatic somatostatin inhibits the release of
both glucagon and insulin.
• The PP cell accounts for about one percent of islet cells and
secretes the pancreatic polypeptide hormone. It is thought to
play a role in appetite, as well as in the regulation of
pancreatic exocrine and endocrine secretions.

20. Insulin 20
• The primary function of insulin is to facilitate
the uptake of glucose into body cells.
• Precisely how insulin facilitates glucose
uptake is not entirely clear.
• However, insulin appears to activate a
tyrosine kinase receptor, triggering the
phosphorylation of many substrates within
the cell.
• These multiple biochemical reactions
converge to support the movement of
intracellular vesicles containing facilitative
glucose transporters to the cell membrane.
• In the absence of insulin, these transport
proteins are normally recycled slowly
between the cell membrane and cell interior.
Insulin triggers the rapid movement of a pool
of glucose transporter vesicles to the cell
membrane, where they fuse and expose the
glucose transporters to the extracellular fluid.
• The transporters then move glucose by
facilitated diffusion into the cell interior
(membrane). Intracellular glucose
transporters.

21. Goiter 21
• The accumulation of colloid
increases the overall size of the
thyroid gland, a condition called
a goiter.

22. Hypothyroidism and Hyperthyroidism 22
• Called hypothyroidism, the
condition is characterized by a
low metabolic rate, weight gain,
cold extremities, constipation,
reduced libido, menstrual
irregularities, and reduced
mental activity.
• In contrast, hyperthyroidism—
an abnormally elevated blood
level of thyroid hormones—is
often caused by a pituitary or
thyroid tumor.

23. Grave’s Disease 23
• In Graves’ disease, the hyperthyroid
state results from an autoimmune
reaction in which antibodies
overstimulate the follicle cells of the
thyroid gland.
• Hyperthyroidism can lead to an
increased metabolic rate, excessive
body heat and sweating, diarrhea,
weight loss, tremors, and increased
heart rate.
• The person’s eyes may bulge (called
exophthalmos) as antibodies produce
inflammation in the soft tissues of the
orbits.
• The person may also develop a goiter.

24. Hyperparathyroidism 24
• Abnormally high activity of the
parathyroid gland can cause
hyperparathyroidism, a disorder caused
by an overproduction of PTH that results
in excessive calcium reabsorption from
bone.
• Hyperparathyroidism can significantly
decrease bone density, leading to
spontaneous fractures or deformities.
• As blood calcium levels rise, cell
membrane permeability to sodium is
decreased, and the responsiveness of the
nervous system is reduced.
• At the same time, calcium deposits may
collect in the body’s tissues and organs,
impairing their functioning.